The present invention relates to the field of borehole drilling, and especially to the field of geothermal borehole drilling. Boreholes may be drilled into the earth for various reasons including the extraction of water, minerals, other liquids (such as petroleum), or gases (such as natural gas). Geothermal drilling generally involves drilling a borehole into the earth in order to access the internal heat of the earth. In various applications, heat may be extracted from the earth and removed to the surface or the earth may be used as a heat sink and heat from the surface may be deposited in the earth.
Geothermal drilling often requires boreholes of greater depth than those required for extraction of desirable materials. Efforts have been made in the field of geothermal drilling to reach borehole depths greater than previously possible. With increased depth, an increase in heat and pressure may be experienced. Seals and bearing surfaces within a drill bit may deteriorate faster by an increased amount of heat and pressure. In addition, as a borehole increases in depth, there is a greater chance for debris to infiltrate bearing cavities and surfaces causing the bearings to wear faster.
U.S. Pat. No. 4,158,394 to Ernst et al., which is herein incorporated by reference for all it contains, discloses a system for lubricating bearings in a drilling apparatus including a roller bit with at least one pivot and a cutting roller rotatably supported on the pivot by bearings. A cavity or chamber is formed in the roller bit for a non-compressible flushing liquid. The flow channel which communicates with the chamber at one end and the bearing cavity at the other end, provides a flow path for the flushing liquid to the bearing cavity. In one form the flushing liquid discharges to the bearing cavity at a point remote from an annular gap between the outer axial end face of the cutting roller and the roller bit. In another embodiment circumferentially spaced discharge ports are located between the bearings so that a portion of the flushing liquid is discharged to the environment and the remainder flows through the bearings and out the annular gap.
U.S. Pat. No. 5,513,711 to Williams, which is herein incorporated by reference for all it contains, discloses a rotary cone drill bit for forming a borehole including a support arm-cutter assembly. A support arm is integrally formed with the drill bit's body with a spindle machined integral thereto. The assembly includes a cutter with a cavity for receiving the spindle. An inner seal gland is formed between the spindle and a wall of the cavity. An elastomeric seal is disposed in the inner seal gland to form a first fluid barrier between. An outer seal gland is formed between the spindle and the cavity wall and between the inner seal gland and the borehole. A ring is disposed in the outer seal gland to rotate with the cutter. The ring has a peripheral hole therethrough. A gas conduit is disposed within the support arm for directing a flow of a gas, such as air, into the outer seal gland. From the outer seal gland, the gas is directed through the hole in the ring and exits into the borehole to form high velocity jets of air to clean a mating surface between the arm and the cutter preventing borehole debris from entering the inner seal gland.